Imaging elements are generally complicated systems comprising a support, adhesion or tie layers, image recording layers and auxiliary layers. The multiple layers required to achieve the desired performance results in a complicated coating process with severe requirements for adhesion to the support and between layers. U.S. Pat. No. 2,627,088, e.g., describes manufacturing process and general difficulty in adhesion to poly(ethylene terephthalate) film base.
Adhesion of the imaging and auxiliary layers to a polymer film support has traditionally been achieved through the use of suitable adhesion or tie layers referred to as a subbing system. Such a subbing system generally involves chemical treatment of the polymer surface with an etch or "bite" agent to improve adhesion of a tie layer. Alternatively, it is also known to subject the support to some form of "energetic" treatment prior to coating. Examples of energetic treatments include glowdischarge treatment (GDT or plasma treatment, coronadischarge treatment (CDT), ultraviolet radiation (UV) treatment, electron-beam treatment, and flame treatment. Subsequently, a polymeric tie layer is coated which has good adhesion to the chemically treated surface and to which subsequently applied layers have good adhesion. Some useful compositions for this purpose include polymers containing vinylidene chloride such as vinylidene chloride/methyl acrylate/itaconic acid terpolymers or vinylidene chloride/acrylonltrile/acrylic acid and the like; butadiene-based copolymers, glycidyl acrylate, or methacrylate containing copolymers, or maleic anhydride containing copolymers. These and other suitable compositions are described, for example, in U.S. Pat. Nos. 2,627,088; 2,698,240; 2,943,937; 3,143,421; 3,201,249; 3,271,178; 3,443,950; and 3,501,301. The polymeric subbing layer is in many instances overcoated with an additional subbing layer comprised of gelatin, typically referred to as a gel sub, or a single mixed subbing layer including polymer and gelatin may be used. The gel sub layer provides good adhesion to subsequently coated layers comprising hydrophilic colloid binders.
U.S. Pat. No. 4,141,735 describes a method for heat tempering or annealing a polyester film base roll, at elevated temperatures up to the glass transition temperature of the polyester, to reduce the core-set curling tendency of the film base material. Reduction in core-set curling tendency has become particularly important in connection with supports for films designed for use with the recently introduced Advanced Photo System.TM., which employs relatively small film cartridges.
As disclosed in U.S. Pat. No. 4,141,735, the film base may or may not be coated with one or more adhesion-promoting subbing layers prior to heat treatment to reduce core-set curling tendency. For improved manufacturing efficiencies, it frequently may be desirable to coat the polymer film with subbing layers prior to heat treatment to reduce core-set curling tendencies, especially where such subbing layers may be applied as part of the support manufacturing process itself. In such an in-line subbing process, the polymer support resin may be first melted and extruded onto a highly polished, smooth casting wheel surface and, before the base is stretched and tentered, a polymer subbing layer undercoat or tie layer may be applied onto one of the two surfaces. After drafting and tentering, a gelatin sub may then be coated over the under-coat, dried, and passed through a heating zone for 2 to 3 minutes to be "heat relaxed" for improvement of the film base's dimensional stability. The subbed film base, after being wound in a tight roll, may then be annealed in an oven to reduce the core-set curling tendencies of the flim
Extended heat-treatment or annealing processes to reduce core-set curling tendencies of gelatin subbed films have been found to severely compromise the adhesive property of the gelatin sub to subsequently coated hydrophilic colloid layers, such as silver halide emulsion layers of silver halide photographic elements. It would be desirable to provide a gelatin subbed film support which may be subjected to heat-treatment or annealing for extended periods of time in a rolled form while maintaining adequate adhesion performance of the gelatin subbing layer to subsequently coated imaging element layers.
U.S. Pat. No. 4,235,959 discloses the use of sorbitol and hexanetriol compounds in subbing layers. U.S. Pat. No. 4,407,939 describes subbing layers for photographic polyester film base, comprised of a first subbing layer of a latex styrene-butadiene copolymer, and a second subbing layer containing gelatin derivatives prepared by reacting gelatin to increase the number of carboxylic groups in gelatin. U.S. Pat. No. 4,542,093 describes subbing layers for photographic polyester film base, comprised of a first subbing layer formed of a polymeric compound, and a second subbing layer containing gelatin and water-soluble methyl cellulose or polyvinyl alcohol. U.S. Pat. No. 5,326,689 describes a general description of producing a film base material which exhibits little core-set curl (via heat treatment) and good adhesive properties (via glow discharge surface treatment). U.S. Pat. No. 5,610,001 discloses gel subbing layers with 1,2,6-hexanetriol. None of the above art, however, discloses heat-treated polymer supports comprising gelatin based subbing layers in accordance with the instant invention, wherein we describe materials that can be added to the gel sub formulation to improve the sub's adhesive property after annealing.